The present exemplary embodiment relates to an improved flexible display system. One form of the display may use various types of switchable materials contained in micro-cells formed from a fabric or mesh material. These cells may serve as a spacer between two opposing electrode sheets and may be individually sealed to the electrode sheets on each face. Moreover, the fabric may, in some forms, be implemented as an electrical grid for addressing the micro-cells.
It finds particular application in conjunction with a flexible display medium such as electric paper and the like, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other applications where flexible displays may be used such as in phones, personal digital assistants (PDAs), computer monitors, signage, billboards, . . . etc.
By way of background, there is a need for a low cost, highly flexible electronic display. Flexible displays will be useful in a variety of implementations. Flexible displays typically utilize a medium that can reversibly change appearance upon application of a stimulus and a means to address specific subsections of the medium with the appropriate stimuli, all in a flexible package. For several reasons, it is also generally desirable to microencapsulate the medium.
Electrophoretic displays that use a mesh-like material are known. In this regard, U.S. Pat. No. 5,276,438 teaches the use of a mesh in an electrophoretic display for purposes of color contrast and providing electrical bias. However, the mesh does not function as structure or to define a micro cell area. Moreover, displays of this type do not have the flexibility desired.
One emerging use of more flexible displays resides in electric paper technology. One way to make electric paper possible using traditional electronic display technology is to completely remove the driving electronics from an electronic display package and use external addressing electrodes to write and erase images. This approach both reduces the per unit cost of electric paper sheets and enables the use of cheap, flexible plastic films in place of glass plates for packaging. Multiple electric paper sheets can then be addressed by a single set of external driving electronics, much like multiple sheets of pulp paper are printed on by a single printer.
A known sheet and display system, dubbed Gyricon, is disclosed in various patents and articles, such as U.S. Pat. No. 4,126,854 by Sheridon titled “Twisting Ball Display.” The Gyricon display system is comprised of an elastomeric host layer of approximately 300 micrometers thick which is heavily loaded with rotating elements, possibly spheres, tens of micrometers (e.g., 100 micrometers) in diameter that serve as display elements. Each rotating display element has halves of contrasting colors, such as a white half and a black half. Each bichromal rotating element also has an electric dipole moment, nominally orthogonal to the plane that divides the two colored halves. Each bichromal rotating element is contained in its own cavity filled with a dielectric liquid. Upon application of an electric field between electrodes located on opposite surfaces of the host layer, the rotating elements will rotate depending on the polarity of the field, presenting one or the other colored half to an observer.
A Gyricon sheet has many of the requisite characteristics of electric paper, namely, bistable image retention, wide viewing angle, thin and relatively flexible packaging, and high reflectance and resolution. U.S. Pat. No. 5,389,945 issued to Sheridon on Feb. 14, 1995, and titled “Writing System Including Paper-Like Digitally Addressed Media and Addressing Device Therefor,” describes an electric paper printing system that employs independent, external addressing means to put images on the Gyricon sheets. The external addressing means is described as a one-dimensional array of electrodes connected, either directly or by wireless technology, to modulating electronics. As the one-dimensional array is scanned across the sheet, modulating electronics adjust the potential at the individual electrodes, creating electric fields between the electrodes and an equipotential surface. An image is created in the sheet according to the magnitude and polarity of the electric fields.
To improve performance, more recent embodiments of these sheets advantageously incorporate charge-retaining islands thereon. U.S. Pat. No. 6,222,513 B1, issued Apr. 24, 2001 and entitled “Charge Islands for Electric Paper and Applications Thereof” describes electric paper having these features. Turning now to FIG. 1, an exemplary Gyricon sheet of this type is shown. The Gyricon sheet is comprised of the following elements: a sheet 300, a first encapsulating layer 302 patterned with conductive charge-retaining islands 306, and a second encapsulating layer 304 that may or may not be patterned with charge-retaining islands.
Together, the first encapsulating layer 302 and the second encapsulating layer 304 do the following things: indefinitely contain a sheet 300, provide at least one transparent window through which the sheet 300 can be viewed, and provide at least one external surface patterned with charge retaining islands 306 that can be addressed with an external charge transfer device. The first encapsulating layer 302 and second encapsulating layer 304 could take the form of thin plastic sheets that are sealed or fastened around the perimeter of the sheet 300. The second encapsulating layer 304 need not be entirely separate from the first encapsulating layer 302. The second encapsulating layer 304 could simply be an extension of the first encapsulating layer 302, folded over and around the edge of the sheet and then sealed or fastened around the remaining perimeter. The first encapsulating layer 302 and second encapsulating layer 304 could also take the form of a coating, applied by spraying, or some other method to hold the contents of the sheet 300.
FIG. 1 also shows a pattern for the charge retaining islands 306 of the outer surface of the first encapsulating layer 302. Charge-retaining islands 306 have square perimeters and are organized in a regular two-dimensional array. Narrow channels 303 of insulating material separate the charge-retaining islands 306. The channels 303 serve to isolate the charge-retaining islands 306, preventing migration of charge laterally across the encapsulating sheet, and should be small with respect to the charge-retaining islands 306, so that the maximum possible area of the display is covered with conductive charge-retaining material.
Referring to FIG. 2, in U.S. application Ser. No. 10/927,691, filed Aug. 27, 2004, entitled “Disordered Three-Dimensional Percolation Technique for Forming Electric Paper,” naming Michael B. Heaney and Gregory P. Schmitz as inventors, an electric paper structure 104 is illustrated having a single layer, or sheet, of relatively disordered particles that heretofore were separated as uniquely formed layers in electric paper structures. In this regard, the single layer includes display elements 106, such as bistable pixel structures and conductive particles 108, both preferably embedded in an insulating matrix of material 110 (e.g., non-conductive particles).The display elements 106 take the exemplary form of microencapsulated bichromal spheres and the conductive particles 108 serve as both conductive islands 114 and as a ground plane 118. The conductive particles 108 form a discontinuous random layer of conductive islands on one side 112 of the sheet, and a continuous electrically conductive percolative network or matrix, or ground plane 118 on the other side of the sheet 116. This is accomplished by varying the effective percolation threshold across the thickness of the sheet 104. That is, particle ratios on one side of the sheet 112 are below the percolation threshold (e.g., forming the conductive islands 114) while the particle ratios on the other side 116 are above the percolation threshold (e.g., forming the ground plane 118).